Process of electroplating an adherent chromium electrodeposit on a chromium substrate

Abstract

What is described herein is a method of electroplating an adherent chromium deposit on a chromium substrate. The process is characterized by chemically oxidizing the chromium substrate before starting the electrodeposition of chromium thereon. A suitable chemical oxidizing agent is hydrogen ion, which can be furnished by a dilute acid solution. The invention is applicable to any chromium electroplating bath, including high energy efficient chromium baths, such as HEEF-40 baths, which are presently in commercial use.

What is claimed is: 
     
       1. In a method of electroplating an adherent chromium deposit on a chromium substrate, from a chromium electroplating bath the step which comprises chemically oxidizing the chromium substrate with hydrogen ion before electrodepositing chromium thereon from a conventional sulfate, mixed catalyst or other high energy efficient chromium electroplating bath, said chemical oxidizing being evidenced by hydrogen evolution and formation of a gray, green-black film on the surface of the chromium substrate. 
     
     
       2. A method according to claim 1 wherein said chemical oxidizing is carried out in a dilute acid solution. 
     
     
       3. A method according to claim 2 wherein said acid is an inorganic or carboxylic acid. 
     
     
       4. A method according to claim 3 wherein said acid is sulfuric acid, hydrochloric acid, phosphoric acid, boric acid, acetic acid, methane sulfonic acid or benzene sulfonic acid. 
     
     
       5. A method according to claim 1 wherein a cathodic current is briefly applied to the chromium substrate before said chemical oxidizing step. 
     
     
       6. A method according to claim 1 wherein said chemical oxidizing step is carried out after an interruption in the chromium plating process and before restarting chromium plating. 
     
     
       7. A method according to claim 1 wherein any oxide film which is present on the chromium substrate is removed chemically or electrolytically before chemically oxidizing the chromium substrate. 
     
     
       8. A method to claim 7 wherein said oxide film is removed anodically in an electrolyte.